DOCUNEIT RESUME ED 055 808 SE 012 075 AUTHOR Bernstein, Jeremy TITLE The Elusive Neutrino, Understanding the Atom Series. INSTITUTION Atoaic Energy Commission, Oak Ridge, Tenn. Div. of Technical Information. PUB DATE 69 NOTE 83p. AVAILABLE FROMUSAEC, P. O. Box 62, Oak Ridge, Tennessee, 37830 (Free) EDRS PRICE 1F-$0.65 HC-$3029 DESCRIPTORS *Atomic Theory; Instructional Materials; *Measurement Techniques; *Nuclear Physics; Radiation; Resource Materials; Science History; *Secondary School Science IDENTIFIERS Fundamental Particles ABSTRACT This booklet is one of the booklets in the "Understanding the Atom Series" published by the U. S. Atomic Energy Commission for high school science teachers and their students. The discovery of the neutrino and the research involving this important elementary particle of matter is discussed. The introductory section reviews topics basic to the understanding of neutrino research: the electron, isotopes, wave character of the electron, spin, the neutron, transformation of particles, the photon, electromagnetic properties, interactions, and relativistic mass. The major portion of the discussion describes how the existence of neutrinos was confirmed, including such concepts as the lass of conservation, the paradox of the energy-momentum balance, perticle-antiparticle annihilation, and other topics. Numerous photographs and diagrams are utilized and a list of suggested references is included. OM U.S. DEPARTMENT OF HEALTH, EDUCATION & WELFARE OFFICE OF EDUCATION -HIS DOCUMENT HAS BEEN REPRO- )UCE0 EXACTLY AS RECEIVED FROM -HE PERSON OR ORGANIZATION ORIG- NATING IT. POINTS OF VIEW OR OPIN- ONS STATED DO NOT NECESSARILY IEPRESENT OFFICIAL OFFICE OF EDU- :ATION POSITION OR POUCY. The Elusive Neutrino Jeremy Bernstein I US.ATOMIC ENERGYCOMMISSION/Division of Technical Information The Understanding the Atom Series Nuclear energy is playing a vital role in thelife of every man, woman, and child inthe United States today. In the years ahead it willaffect increasingly all the peoples of the earth. It is essential that all Americans gain anunderstanding of this vital force if they are to dischargethoughtfully their responsibilities as citizens and if they are to realizefully the myriad benefits that nuclear energy offers them. The United States Atomic Energy Commissionprovides this booklet to help you achieve suchunderstanding. 444'1144e eL44..°4-41-- IFEdward J. Brunenkant, Director Division of Technical Information . a a a -.. s M. -M. THE ELUSIVE NEUTRINO by Jeremy Bernstein CONTENTS INTRODUCTION Greek Origins 19th Century Revival The Electron Isotopes Wave Character of the Electron Spin The Neutron Transformation of Particles JUST GIVE THE NEWS The Photon Electromagnetic Properties Interactions Mass Spin HOW DO YOU KNOW? Experimental Method Conservation Laws Quantitative Study of Radioactive Nuclei Decay Paradox of the Energy-Momentum Balance Enrico Fermi's Little Neutra! One Particle-Antiparticle The Conservation of Leptons The Fall of Parity THERE ARE FOUR OF THEMI Neutrino Catching Cowan-Reines Experiments Conservation of Lepton Number in Neutrino Reactions Hideki Yukawa and the Strong Interactions The Muon and the Conservation Laws TWINKLE, TWINKLE, LITTLE STAR SUGGESTED REFERENCES United States Atomic Energy Commission Division of Technical Information lathrary of Congress Catalog Card Number: 71-601702 1969 Vil,',14 i,'il I eJkill11) vd i , ,\ , l!' 1 1 140OWN1144tib,14411 I 1 Ii NIAO(J' I i Il fl'i'lgi I I j1 411 N.1 I i I lty0W I P'11 1°4Nilc)41H I W III i?I11111 1 oi P%4ci I 11) N'i' ci 1 14 tl., W, THE ELUSIVE NEUTRINO by Jeremy Bernstein INTRODUCTION If a physicist were asked, "What is a neutrino?", he would reply that it is an elementary particle, which conjures up the image of a tiny liard ball. The neutrino is nothing like this, but the conception of an elementary particle has grown out of experience and language ap- propriate to billiard balls. A billiard ball has size, mass (or weight), and perhaps electric charge.* If set in motion it has momentum and kinetic energy.t At rest it has an energy given by Einstein's celebrated equation E = mc2 - Size, mass, and electric charge are macroscopic properties of matterone can ascribe these properties to any unit of matter, even the tiniest units such as the neutrino as well as the lzrgest such as galaxies. As we shall see later there are other properties, such as spin, wavelength, helicity, lepton number, etc., which exhilat themselves most clearly in the subatomic domain of the elementary particles and which are not useful in the description of real billiard balls. *A billiard ball also has color, but this is not a property that one can ascniee to elementary particles, which can't even be seen with the naked eye. Color is an example of a macroscopic propertya property that is manifested through the behavior of millions of atoms acting in concert. Other macroscopic properties are taste, smell, and temperature. tKinetic energy is the energy associated with the motion of material bodies. 1 Greek Origins The modern view of an elementary particle did not arise full p-own like Venus in the seashell. It has a history extending back to the Greeks. The Greek atomists, notably Democritus and his school, came upon the notion of elementary particles by pure reasona dangerous path in science for as often as not the pure reason of today is the scientific nonsemse of tomorrow" They reasoned that mattercould not be subdivided without limit. If one continued breakincr a twit,.e),one would eventually come to an elemental twig, which could not be subdivided further. ThQe elemental units of matter were called atoms (atom means indivisible in Greek) and were the building blocks out of which ordinary matter was constructed. There was in the Greek atomic idea something that has been with us ever since and one which is crucial tomodern science: The regularities in our everyday experience can be explained by postulating the existence of a new domain of phenomena. These atoms are simpler than the things we see around us and, although rot directly observable, control the behavior of the things that we do see- For example, we explain that an object is hot because it is composed of atoms in motion and the enerwv of this motion produces the effect that we call heat. 19th Century Revival For nearly 2000 years the idea of the atom lav dormant and was not revived in its present form until the 19th century.The impetus for the revival was chemists, who observed that chemical compounds always contain their constituents in constant proportions by weight however small the sample.. For example, if you hook tennis balls and golf balls together, pairing always one tennis and one golf ball, then any sample of 41:hese molecules will contain, by weight, the same ratio of tennis to golf ball weights_ The new atomists like John Dalton must have had some picture like this in mind to explain the law of constant proportions- Many celeErated scientists thought that this was pure nonsense until Einstein, in 1905, explained the Brownianmotionthe apparently random motion of tiny objects suspexided in a colioidal liquidas being the effect of the constant bombardment these objects suffered from the molecules or atoms in the liquid_ This was the first time since the Greeks that invisible atoms were used to explain a complex visible phenomenon in physics. *They also argued, for example, that "nature abhors a vacuum", but intergalactic space is nearly pure vacuum! 2 lie14*/"It'llrtiO I F 1 4 4 J i I 1 ' iI1 k 1 , A 1 ! 1 ; iI. If4t, $I 1 : 0, , t I 6 I # is 6 ' V i . I .4t,,t1 01 '. 0 4 I' ; t ..1 VP 4 I t 4 "P' opI gg 4 4/ Ot'i° .4'1. .,, itt' Pi .4,14 h . t., il r i t . C I k k '''. 41 .1 '' it' !it4° /11.'1 ' $I° II/ LI 1 l',. 4 / t i 0 1Pio I 1,011...1.;41g;.,11,,,i'l" r, ill1 40 ,141, ... ,.. lii1,114+i.i,IkP;'' 1P ' ,04 f 414. 0 ,g, ' , r14 4i '. if.1.,i .9 ' I .1 11,1 ';.444.111$0,$4 $i $ii .:1'-i'r'I't . 1 ii 11 1. .,, ,'111 1,106 4,P, f4I II.. :11.: 4. k1#1°,' 1 I" ' 1'I, tl' t l' ! ' et' '.#11#11,.:13 ' Ili#1, a 1 44444444 ,- , .; ' h loi 4II., 'itip.,,IPili I 1 1 1 i 1.14'. 'tt 14 I 114Iiii A 4. iii $,' :, 44 : Ii 1 144411 . I 11 1 ' 1 If44' Oili1 9 I.illiigi p[., i :1 Ii t 1 I 11°) I i !'' , , ' . ,II11A,'i' iiii ! .1 4 "fidlilil t 11' if diii4 i ,. ':i '1 .i' ,,,i i.1111. .':1,./,$.:.:,1i:11 fi,.4#0%,MI;)?,i 1J'1;t1!.A ki I fle;:41/111;;'':v),,11'1fillil' 103 iliVi ,,,,*`,1 t iiifitill 111i, I'Olio;i;; 1 441'444 . (4. /1.71 4.414 ,4,t4''Cilllii4,:I'll PO,littifIti 1,1 .4 L ' i, , it {1 ' iii.°1/4.4 .;i11 .', ' t 1 1 "PI i ti ,,i'iI'll- '1'1' 'OA r' 1 III I 111 I , ' i I1. ' 1 ,111 I I .111'16' ,A if a 11' 1 41II 1, I '0.4IFPl.' .1'' i.''411 c!,11 fl l'Ir 1,1 4 Ta , 1,1 1 1 i l'h'il I 1 41,1+i'' 4" 41, ' 1,,1 , .1, I Ai I , I r 'I'll r/ti I ' ,, /ill I, I... :11 All ' ' t! 'I.,,4.,...11.i11 t Ill IA ,11 oryr.fl 4 ,,I , 'Aic 1 .1 : 1 1 ill / lilii II 1",., "44 11'.1,.1,,i ,'. 11.!..41171. I t, 11 411 Irl- , ., i ",' .